Gas assisted injection moulding is a thermoplastic moulding process in which an inert gas is injected into a mouldable material after the moulded material enters a mould. The gas does not mix with the mouldable material but is intended to remain in the middle of the thicker sections of the moulding. By controlling the gas pressure, the quantity of mouldable material injected into mould and the rate of gas flow, a hollow portion can be formed within the moulded part. The gas pressure compensates for the tendency of the mouldable material to shrink at the thicker parts of the moulding, preventing warping and reducing stress. Gas pressure can be relieved before opening the mould.
It has been proposed in the past that the introduction of pressurised gas into the mould may be through the same nozzle that introduces the mouldable material in the part. In the production of some parts it is desirable to induce the pressurised gas at a different location as that of which the mouldable material is introduced. In the past, a gas pin has been used for this purpose, however, this is not applicable where it is desired to produce a functional cavity.
By the term “functional cavity” in this specification it is generally intended to mean a cavity which is formed in an injection moulded part which in the finished product is used for a defined or useful purpose. The defined or useful purpose may be for instance to enable the joining of two ducts or tubes retained in the mould and extending into the mould cavity and moulded into a part to provide a fluid connection between them within the functional cavity. The functional cavity, for instance, may be used to mix two fluid flows or to enable fluid flow from one duct to another within the moulded part.